An image forming apparatus has been known which has a fixing device including a heater and a temperature sensor and is configured to control a temperature of the heater on the basis of a signal from the temperature sensor. Specifically, the image forming apparatus is configured to execute control (hereinafter, referred to as “on-off temperature control of the healer”) of continuing to energize the heater for a time period in which a detected temperature acquired on the basis of the signal from the temperature sensor is equal to or lower than a reference temperature and continuing to stop the energization of the heater for a time period in which the detected temperature exceeds the reference temperature.
For example, in IEC/EN61000-3-3 that is a standard of a flicker, as an index of the flicker, a flicker value (a short-term flicker value (Pst, a long-term flicker value (Plt)) indicative of a periodic voltage change, a maximum relative voltage change (dmax) indicative of an instantaneous voltage change due to inrush current, and the like are exemplified. In the on-off temperature control of the heater, an undershoot situation that the detected temperature considerably falls short of the reference temperature due to a delay (hereinafter, referred to as “temperature delay”) of the detected temperature with respect to an actual temperature such as a response delay of the temperature sensor occurs. For this reason, the temperature of the heater greatly varies, so that current to be output from the heater considerably changes. As a result, particularly, the maximum relative voltage change (dmax) may not be reduced.